2022年经济学人 大陆形成新学说(2)（在线收听）

The team traversed the craton to collect zircon crystals, a mineral with two properties ideally suited to the task.

研究小组穿越古陆核采集锆石晶体，这种矿物有两种特性，非常适合这项任务。

First, their content of radioactive uranium decays to lead at a rate that can be used to calculate their age.

首先，他们的放射性铀含量衰减成铅的速度可以用来计算他们的年龄。

And second, the isotopes of oxygen found within their structure are representative of the environment in which they grew.

其次，在它们的结构中发现的氧同位素代表了它们生长的环境。

Zircons whose ratio of oxygen-18 to oxygen-16 is 0.5% higher than found in seawater, for example, would have originated far below Earth’s surface.

例如，在海水中发现的氧-18和氧-16的比率比高0.5%的锆石可能起源于地球表面以下很远的地方。

Those with values closer to those found in seawater formed much nearer the crust.

那些与海水中发现的值更接近的物质形成于更接近地壳的地方。

Analysis led the researchers to conclude that the oldest crystals on the Pilbara -- those formed around 3.5bn years ago -- must have originated close to the surface.

通过分析，研究人员得出结论，皮尔巴拉上最古老的晶体--大约形成于35亿年前--一定起源于靠近地表的地方。

This favours impact formation, as zircons transported by mantle plumes would have more profound origins.

这有利于撞击的形成，因为地幔热柱搬运的锆石具有更深的起源。

“Giant impacts plus water is a really good way of making a continent,” says Dr Johnson.

约翰逊博士说：“巨型撞击加上水是形成大陆的一种非常好的方式。”

The textbooks will not be rewritten overnight.

教科书不会在一夜之间改写。

Marion Garcon, a geologist at Clermont-Auvergne University in France, finds the evidence of impact formation plausible on a local scale, but says more evidence will be needed to extrapolate it planet-wide.

法国克莱蒙特-奥弗涅大学的地质学家马里恩·加尔孔认为，在局部范围内，撞击形成的证据是可信的，但他表示，需要更多证据才能在全球范围内推断这一点。

Fortunately, this can be done.

幸运的是，这是可以做到的。

Ancient continental fragments exist in other parts of Australia as well as Canada and South Africa.

古老的大陆碎片存在于澳大利亚其他地区、加拿大和南非。

Analyses of their constituent zircons could well provide valuable supporting evidence that Earth’s continents owe their existence to bodies from outer space.

对其构成的锆石的分析很好地提供有价值的佐证，证明地球大陆的存在应归功于来自外太空的天体。

But the authors will also need to explain why zircons previously found at other, even older, sites do not display the same telltale signature of impact.

但作者还需要解释，为什么之前在其他更古老的地点发现的锆石没有显示出相同的撞击迹象。

This work could be significant in other ways.

这项工作可能在其他方面具有重要意义。

While the rate of asteroid collisions experienced by early Earth generally declined over time, it may have spiked some 3.9bn years ago during a postulated event known as the Late Heavy Bombardment (lhb).

虽然早期地球经历的小行星碰撞的概率通常会随着时间的推移而下降，但在大约39亿年前的一次假定事件-晚期重轰击(LHB)期间，小行星碰撞的概率可能达到了峰值。

What are taken by some as signs of the lhb pockmark the static surfaces of Mars and the Moon.

一些人认为LHB的迹象在火星和月球的静态表面上留下了凹坑。

Earth’s constant ructions, however, will have destroyed any signs of it.

然而，地球持续不断的骚动将摧毁它的任何迹象。

If Dr Johnson is right, then the formation of the continents could be the first earthly evidence of one of the solar system’s most dramatic moments.

如果约翰逊博士是正确的，那么大陆的形成可能是太阳系最戏剧性时刻之一的第一个地球证据。